Integrally foamed microstructured article

ABSTRACT

The invention is directed in part to an article that includes a polymer foam having a surface with surface microstructures, the surface microstructures have at least one extent or dimension of about 10 microns or more, preferably 50 microns or more. A maximum extent (unless it is a continuous rib-like structure) the microstructure is about 300 microns or less, preferably 200 microns or less, and generally a maximum height of 1000 microns or less, preferably 750 microns or less and a minimum height of 200 microns or more, preferably 300 microns or more. The foamed article may be provided in a variety of shapes, including a rod, a cylinder, a sheet, etc. In a preferred embodiment where the foam is provided in the form of a sheet, the foam has a pair of major surfaces, one or both of which can be provided with surface microstructures. The foam backing and microstructures include a plurality of voids, which voids are preferably of a mean size substantially less than the smallest cross-sectional dimension or extent of the microstructures.

BACKGROUND OF THE INVENTION

This invention relates to preparing extruded articles having surfacemicrostructures formed with a microcellular polymer foam. Generally, apolymer foam includes a polymer matrix and is characterized by a densitythat is lower than the density of the to polymer matrix itself. Densityreduction is achieved in a number of ways, including through creation ofgas-filled voids in the matrix (e.g., by means of a blowing agent). Thefoam void is of a size less than that of the microstructures.

In order to improve the mechanical properties of standard cellularfoamed materials, a microcellular process was developed formanufacturing foamed plastics having greater cell densities and smallercell sizes. Such a process is described, for example, in U.S. Pat. No.4,473,665. The process presaturates the plastic material with a uniformconcentration of a gas under pressure. A sudden induction ofthermodynamic instability then nucleates a large number of cells. Forexample, the material is presaturated with the gas and maintained underpressure at its glass transition temperature. The material is suddenlyexposed to a low pressure to nucleate cells and promote cell growth to adesired size, depending on the desired final density, thereby producinga foamed material having microcellular voids, or cells, therein. Thematerial is then quickly further cooled, or quenched, to maintain themicrocellular structure. Such a technique tends to increase the celldensity, i.e., the number of cells per unit volume of the parentmaterial, and to produce much smaller cell sizes than those in standardcellular structures. The resulting microcellular foamed materials thatare produced, using various thermoplastics and thermosetting plastics,tend to have average cell sizes in the range of 3 to 10 microns, withvoid fractions of up to 50% of the total volume and maximum celldensities of about one billion voids per cubic centimeter of the parentmaterial.

Microcellular foamed plastic materials are also described in U.S. Pat.No. 4,761,256 which describes a web of plastic material impregnated withan inert gas. The web is reheated at a foaming station to inducefoaming, the temperature and duration of the foaming process beingcontrolled prior to the generation of the web to produce the desiredcharacteristics. The process is designed to provide for production offoamed plastic web materials in a continuous manner. The cell sizes inthe foamed material is stated to be within a range of from 2 to 9microns in diameter.

U.S. Pat. No. 5,334,359 describes foamed materials which can be ofsmaller cell sizes, e.g., 1.0 micron or less. The materials alsoallegedly have a wide range of void fraction percentages from very highvoid fractions (low material densities) up to 90%, or more, to very lowvoid fractions (high material densities) down to 20%, or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a first method for forming an extrudedfoamed hook strip in accordance with the invention.

FIG. 2 is a schematic view of a further method used in forming hookstrip in accordance with the present invention.

FIG. 3 is a schematic view of a second method for forming an extrudedhook strip in accordance with the invention.

FIG. 4 is an enlarged perspective view of a hook fastener formed by themethod of FIG. 3.

FIG. 5 is a cross-section photomicrograph of a foamed hook formed by amethod such as shown in FIGS. 1 and 2.

FIG. 6 is a counterexample photomicrograph of a foamed hook formed by amethod in FIGS. 1 and 2.

FIG. 7 is a photomicrograph of a foamed hook formed by a method such asshown in FIG. 3.

FIG. 8 is a photomicrograph of a foamed hook formed by a method such asshown in FIG. 3.

FIG. 9 is a perspective view of a disposable garment using a breathablehook fastener member according to the present invention.

FIG. 10 is a perspective view of a disposable garment using a hookmember according to the present invention.

FIG. 11 is a perspective view of a disposable garment using a hookmember according to the present invention.

FIG. 12 is a perspective view of a feminine hygiene article using a hookmember according to the present invention.

FIG. 13 is a breathable hook fastener of the present invention as aself-engaging structure.

FIG. 14 is a breathable hook fastener of the present invention used as abody wrap.

FIG. 15 is a breathable hook fastener of the present invention used as abody wrap.

SUMMARY OF THE INVENTION

In a first aspect, the invention is directed to an article that includesa polymer foam having a surface with surface microstructures. Thesurface microstructures have at least one extent or dimension of about10 microns or more, preferably 50 microns or more, and preferably amaximum extent (unless it is a continuous rib-like structure) of about300 microns or less, preferably 200 microns or less, and generally amaximum height of 1000 microns or less, preferably 750 microns or lessand a minimum height of 200 microns or more, preferably 300 microns ormore. The foamed article may be provided in a variety of shapes,including a rod, a cylinder, a sheet, etc. In a preferred embodimentwhere the foam is provided in the form of a sheet, the foam has a pairof major surfaces, one or both of which can be provided with surfacemicrostructures. The foam backing and microstructures include aplurality of voids, which voids are of a mean size substantially lessthan the smallest cross-sectional dimension or extent of themicrostructures. The foam can be formed by known blowing agents.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The shape of the foam is dictated by the shape of die and/or the moldsurface if used. Although a variety of shapes may be produced, the foamis typically produced in the form of a continuous or discontinuous sheethaving surface microstructures.

An extrusion process using a single-screw, double-screw or tandemextrusion system may also be used to form the foam using a blowingagent, e.g., a physical or chemical blowing agent. The temperature andpressure conditions in the extrusion are preferably sufficient tomaintain the polymeric material and blowing agent as a homogeneoussolution or dispersion. Preferably, the polymeric materials exit theextruder and are foamed at no more than 30° C. above the meltingtemperature of the neat polymer thereby producing desirable propertiessuch as uniform and/or small cell sizes. When a physical blowing agent,such as CO₂ is used, the polymer is generally initially maintained abovethe melting temperature. The physical blowing agent (preferably in thesupercritical state) is then injected (or otherwise mixed) with themolten polymer and the melt mixture is cooled in the extruder preferablyto an exit temperature that is less than 50° C. above the meltingtemperature or T_(g) of the polymer T<T_(m) (or T_(g))+50° C. while thepressure is maintained at or above 1000 psi (13.8 MPa), preferably 30°C. while the pressure is maintained at or above 2000 psi. Under theseconditions the polymer/blowing agent generally remains in a singlephase. As the melt mixture passes through the die the melt foams andexpands, generating foams with preferably small, uniform cell sizes.When a chemical blowing agent is used, the blowing agent is added to thepolymer, mixed, heated to a temperature above the T_(m) of the polymerto ensure intimate mixing and further heated to an activationtemperature of the chemical blowing agent, resulting in generation ofgasses. The melt mixture is cooled in the extruder preferably in amanner similar to that used for physical blowing agents. A liquid orsolid chemical foaming agent is generally added to the polymer prior toits reaching its molten (T_(m)) state.

A supercritical fluid foaming agent can be defined as a material whichis maintained at a temperature which exceeds a critical temperature andat a pressure which exceeds a critical pressure so as to place thematerial in a supercritical fluid state. In such state, thesupercritical fluid has properties which cause it to act, in effect, asboth a gas and a liquid. Thus, in the supercritical state, such a fluidhas the solvent characteristics of a liquid, but the surface tensionthereof is substantially less than that of a liquid so that the fluidcan diffuse much more readily into a solute material, as in the natureof a gas. For example, it is known that carbon dioxide (CO₂) can beplaced in a supercritical state when its temperature exceeds 31° C. andits pressure exceeds 1100 psi.

When the foam is formed into a microstructured article directly from theextrusion die, the polymer matrices of the invention foams can compriseone or more amorphous polymers or polymer blends as well assemicrystalline polymer. The polymers may be homopolymers or copolymers,including random and block copolymers. The amorphous polymers have aT_(g) with the T_(g) typically an average, (based on the weight percentof each polymer in the mixture), of the glass transition temperatures ofthe component polymers. Suitable amorphous polymers include, e.g.,polystyrenes, polycarbonates, polyacrylics, polymethacrylics,elastomers, such as styrenic block copolymers, e.g.,styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene blockcopolymers (SEBS), polybutadiene, polyisoprene, polychloroprene, randomand block copolymers of styrene and dienes (e.g., styrene-butadienerubber (SBR)), ethylene-propylene-diene monomer rubber, natural rubber,ethylene propylene rubber, polyethylene-terephthalate (PETG). Otherexamples of amorphous polymers include, e.g., polystyrene-polyethylenecopolymers, polyvinylcyclohexane, polyacrylonitrile, polyvinylchloride,thermoplastic polyurethanes, to aromatic epoxies, amorphous polyesters,amorphous polyamides, acrylonitrile-butadiene-styrene (ABS) copolymers,polyphenylene oxide alloys, high impact polystyrene, polystyrenecopolymers, polymethylmethacrylate (PMMA), fluorinated elastomers,polydimethyl siloxane, polyetherimides, amorphous fluoropolymers,amorphous polyolefins, polyphenylene oxide, polyphenyleneoxide-polystyrene alloys, copolymers containing at least one amorphouscomponent, and mixtures thereof.

When the microstructured article is formed by contact with a moldsurface having the microstructures therein the polymer must bemaintained in a molten state following extrusion from the die. Amorphouspolymers generally freeze immediately and are not preferred for thisprocess. Semicrystalline polymers are preferred. For example, high,medium, low and linear low density polyethylene, fluoropolymers,poly(1-butene), ethylene/acrylic acid copolymer, ethylene/vinyl acetatecopolymer, ethylene/propylene copolymer, styrene/butadiene copolymer,ethylene/styrene copolymer, ethylene/ethyl acrylate copolymer, ionomersand thermoplastic elastomers such as styrene/ethylene-butylene/styrene(SEBS), and ethylene/propylene/diene copolymer (EPDM). Preferred arepolyolefins such as polypropylenes or polyethylenes and most preferablyhigh melt strength polyolefins, such as branched polyolefins. These highmelt strength polymers help control the growth of the foam cells withinthe desired range necessary for creating the discrete microstructuresand prevent collapse of the cells during surface microstructureformation if needed. Suitable semi-crystalline materials includepolyethylene, polypropylene, polymethylpentene, polyisobutylene,polyolefin copolymers, Nylon 6, Nylon 66, polyester, polyestercopolymers, fluoropolymers, poly vinyl acetate, poly vinyl alcohol, polyethylene oxide, functionalized polyolefins, ethylene vinyl acetatecopolymers, metal neutralized polyolefin ionomers available under thetrade designation SURLYN (E.I. DuPont de Nemours, Wilmington, Del.),polyvinylidene fluoride, polytetrafluoroethylene, polyformaldehyde,polyvinyl butyral, and copolymers having at least one semi-crystallinecompound. Preferred high melt strength polymers are high melt strengthpolypropylenes which include homo- and copolymers containing 50 weightpercent or more propylene monomer units, preferably at least 70 weightpercent, and have a melt strength in the range of 25 to 60 cN at 190° C.Melt strength may be conveniently measured using an extensionalrheometer by extruding the polymer through a 2.1 mm diameter capillaryhaving a length of 41.9 mm at 190° C. and at a rate of 0.030 cc/sec; thestrand is then stretched at a constant rate while measuring the force tostretch at a particular elongation. Preferably the melt strength of thepolypropylene is in the range of 30 to 55 cN, as described in WO99/61520.

Such high melt strength polypropylenes may be prepared by methodsgenerally known in the art. Reference may be made to U.S. Pat. No.4,916,198 which describes a high melt strength polypropylene having achain-hardening elongational viscosity prepared by irradiation of linearpropylene in a controlled oxygen environment. Other useful methodsinclude those in which compounds are added to the molten polypropyleneto introduce branching and/or crosslinking such as those methodsdescribed in U.S. Pat. No. 4,714,716, WO 99/36466 and WO 00/00520. Highmelt strength polypropylene may also be prepared by irradiation of theresin as described in U.S. Pat. No. 5,605,936. Still other usefulmethods include forming a bipolar molecular weight distribution asdescribed in JI Raukola, “A New Technology To Manufacture PolypropyleneFoam Sheet And Biaxial Oriented Foam Film”, VTT Publications 361,Technical Research Center of Finland, 1998 and in U.S. Pat. No.4,940,736.

Generally, the foamable polypropylenes may comprise solely propylenehomopolymer or may comprise a copolymer having 50 wt % or more propylenemonomer content. Further, the foamable propylenes may comprise a mixtureor blend of propylene homopolymers or copolymers with a homo- orcopolymer other than propylene homo- or copolymers. Particularly usefulpropylene copolymers are those of propylene and one or morenon-propylenic monomers. Propylene copolymers include random, block, andgrafted copolymers, of propylene and olefin monomers selected from thegroup consisting of ethylene, C₃-C₈ α-olefins and C₄-C₁₀ dienes.Propylene copolymers may also include terpolymers of propylene andα-olefins selected from the group consisting of C₃-C₈ α-olefins, whereinthe α-olefin content of such terpolymers is preferably less than 45 wt%. The C₃-C₈ α-olefins include 1-butene, isobutylene, 1-pentene,3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene,3-methyl-1-hexene, and the like. Examples of C₄-C₁₀ dienes include1,3-butadiene, 1,4-pentadiene, isoprene, 1,5-hexadiene, 2,3 dimethylhexadiene and the like.

If high melt strength polymers are used, minor amounts (less than 50percent by weight) of amorphous polymers may be added to the high meltstrength polymer. Suitable amorphous polymers include, e.g.,polystyrenes, polycarbonates, polyacrylics, to polymethacrylics,elastomers, such as styrenic block copolymers, e.g.,styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene blockcopolymers (SEBS), polybutadiene, polyisoprene, polychloroprene, randomand block copolymers of styrene and dienes (e.g., styrene-butadienerubber (SBR)), ethylene-propylene-diene monomer rubber, natural rubber,ethylene propylene rubber, polyethylene-terephthalate (PETG). Otherexamples of amorphous polymers include, e.g., polystyrene-polyethylenecopolymers, polyvinylcyclohexane, polyacrylonitrile, polyvinyl chloride,thermoplastic polyurethanes, aromatic epoxies, amorphous polyesters,amorphous polyamides, acrylonitrile-butadiene-styrene (ABS) copolymers,polyphenylene oxide alloys, high impact polystyrene, polystyrenecopolymers, polymethylmethacrylate (PMMA), fluorinated elastomers,polydimethyl siloxane, polyetherimides, amorphous fluoropolymers,amorphous polyolefins, polyphenylene oxide, polyphenyleneoxide-polystyrene alloys, copolymers containing at least one amorphouscomponent, and mixtures thereof.

In addition to the high melt strength polypropylene, the foam layer maycontain other added components such as dyes, particulate materials, acolorant, an ultraviolet absorbing material, inorganic additives, andthe like. Useful inorganic additives include glass fibers, TiO₂, CaCO₃,mica or high aspect ratio clays such as wollastonite

Either a physical or chemical blowing agent may plasticize, i.e., lowerthe T_(m) and T_(g) of, the polymeric material. With the addition of ablowing agent, the melt mixture may be processed and foamed attemperatures considerably lower than otherwise might be required, and insome cases may be processed below the melt temperature of thepolypropylene. The lower temperature can allow the foam to cool andstabilize (i.e., reach a point of sufficient solidification to arrestfurther cell growth and produce smaller and more uniform cell sizes).

Physical blowing agents useful in the present invention may be anymaterials that are a vapor at the temperature and pressure at which thefoam exits the die. A physical blowing agent may be introduced, i.e.,injected into the polymeric material as a gas or supercritical fluid.Flammable blowing agents such as pentane, butane and other organicmaterials may be used, but non-flammable, non-toxic, non-ozone depletingblowing agents such as carbon dioxide, nitrogen, water, SF₆, nitrousoxide, argon, helium, noble gases, such as xenon, air (nitrogen andoxygen blend), and blends of these materials are preferred because theyare easier to use, e.g., fewer environmental and safety concerns. Othersuitable physical blowing agents include, e.g., hydrofluorocarbons(HFC), hydrochlorofluorocarbons (HCFC), and fully- or partiallyfluorinated ethers.

Chemical blowing agents are added to the polymer at a temperature belowthat of the activation temperature of the blowing agent, and aretypically added to the polymer feed at room temperature prior tointroduction to the extruder. The blowing agent is then mixed todistribute it throughout the polymer in unactivated form, above the melttemperature of the polypropylene, but below the activation temperatureof the chemical blowing agent. Once dispersed, the chemical blowingagent may be activated by heating the mixture to a temperature above theactivation temperature of the agent. Activation of the blowing agentliberates gas either through decomposition (e.g., exothermic chemicalblowing agents such as azodicarbonamide) or reaction (e.g., endothermicchemical blowing agents such as sodium bicarbonate-citric acidmixtures), such as N₂, CO₂ and/or H₂O, yet cell formation is restrainedby the temperature and pressure of the system. Useful chemical blowingagents typically activate at a temperature of 140° C. or above.

Examples of chemical blowing agents include synthetic azo-, carbonate-,and hydrazide based molecules, including azodicarbonamide,azodiisobutyronitrile, benzenesulfonhydrazide, 4,4-oxybenzenesulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, bariumazodicarboxylate, N,N′-dimethyl-N,N′-dinitrosoterephthalamide andtrihydrazino triazine. Specific examples of these materials are CelogenOT (4,4′oxybis(benzenesulfonylhydrazide)). Other chemical blowing agentsinclude endothermic reactive materials such as sodium bicarbonate/citricacid bends that release carbon dioxide. Specific examples include. ReedyInternational Corp SAFOAM products.

With either a chemical or physical blowing agent, as the melt mixtureexits the extruder through a shaping die, it is exposed to the muchlower atmospheric pressure causing the blowing agent (or itsdecomposition products) to expand. This causes cell formation resultingin foaming of the melt mixture. When the melt mixture exit temperatureis at or below 50° C. above the T_(m) of the neat polymer, the increasein T_(m) of the polymer as the blowing agent comes out of the solutioncauses crystallization of the polypropylene, which in turn arrests thegrowth and coalescence of the foam cells within seconds or, mosttypically, a fraction of a second. This preferably results in theformation of small and uniform voids in the polymeric material. When theexit temperature is no to more than 50° C. above the T_(m) of the neatpolymer, the extensional viscosity of the polymer increases as theblowing agent comes out of the solution and the polypropylene rapidlycrystallizes. When a high melt strength polymer is used, the extensionalthickening behavior is especially pronounced. These factors arrest thegrowth and coalescense of the foam cells within seconds or, mosttypically, a fraction of a second. Preferably, under these conditions,the formation of small and uniform cells in the polymeric materialoccurs. When exit temperatures are in excess of 50° C. above the T_(m)of the neat polymer, cooling of the polymeric material may take longer,resulting in non-uniform, unarrested cell growth. In addition to theincrease in T_(m), adiabatic cooling of the foam may occur as theblowing agent expands.

The amount of blowing agent incorporated into the foamable polymermixture is generally chosen to yield a foam having a void content inexcess of 10%, more preferably in excess of 20%, as measured by densityreduction; [1−the ratio of the density of the foam to that of the neatpolymer]×100. Generally, greater foam void content reduces the foamdensity, weight and material costs for subsequent end uses.

Preferably, the formed foam is oriented such as by uniaxial or biaxialstretching in mutually perpendicular directions at a temperature abovethe alpha transition temperature and below the melting temperature ofthe polymer matrix (e.g., polypropylene). Generally, in biaxialstretching, the film is stretched in one direction first and then in asecond direction perpendicular to the first. However, stretching may beeffected in both directions, simultaneously if desired. If biaxialorientation is desired, it is preferable to simultaneously orient thefoam, rather than sequentially orient the foam along the two major axes.In a typical sequential orientation process, the film is stretched firstin the direction of extrusion over a set of rotating rollers and thenstretched in the direction transverse thereto by means of a tenterapparatus. Alternatively, foams may be stretched in both the machine andtransverse directions in a tenter apparatus. Foams may be stretched inone or both directions 3 to 75 times total draw ratio (MD×CD) forbiaxial stretching or 1-10 times for uniaxial stretching. Generallygreater orientation is achievable using foams of small cell size; foamshaving cell size of greater than 100 microns are not readily biaxiallyoriented more than 20 times, while foams having a cell size of 50microns or less could be stretched up to 75 times total draw ratio. Inaddition foams with small to average cell size exhibit greater tensilestrength and elongation to break after stretching.

The final thickness of the foam will be determined in part by theextrusion thickness, the degree of orientation, and any additionalprocessing. The present invention provides thinner foams than aregenerally achievable by prior art processes. Most foams are limited inthickness by the cell size. In the present invention, the small cellsizes (100 microns or less) in combination with the orientation allows afoam sheet thickness of 25 microns to 1000 microns, and foam sheets of25 microns to 100 microns are readily prepared. This is extremelydesirable with microstructured hook structures as a soft conformablebacking is obtained that can be used in many uses where contact with anactive wearer (e.g., a person) is desired or possible. Specifically, thefoamed hook with microstructured hooks can be used with disposableabsorbent articles such as diapers as a closure tab, which is soft tothe touch and is aesthetically pleasing due to its pearlescentappearance. Other uses where a hook strip or tab would be in contactwith a sensitive surface would include medical wrap, sport wraps,headbands, produce wraps and feminine hygiene articles. Suitablebackings can have a softness of from 10 to 2000 Gurley units, preferablyfrom 10 to 200 Gurley units.

Preferably, the foam can have cell sizes of 2 to 100 microns, preferably5 to 50 microns. The foam may alternatively, or additionally, have acell size distribution with a polydispersity from 1.0 to 2.0, preferablyfrom 1.0 to 1.5, more preferably from 1.0 to 1.2.

The polymer foam surface microstructures generally have at least onecross-sectional extent of about 10 microns or more, preferably 50microns or more, and if a discrete microstructure rather than acontinuous or discontinuous rib or the like the microstructure couldhave a maximum extent of about 300 microns or less, preferably 200microns or less, a maximum height of 1000 microns or less, preferably750 microns or less and a minimum height of 200 microns or more,preferably 300 microns or more. An extent of the microstructure isgenerally considered a dimension of the microstructure from one face toan opposite or opposing face or interface (e.g. the base of themicrostructure where it is joined to the backing) and could be a width,a height or a thickness dimension or some other dimension at someportion of the microstructure.

The microstructures smallest cross-sectional dimension is generally 10microns or more. The smallest cross-sectional dimension generally wouldexclude the tips of a microstructure, and would generally be measured ata distance of 10 microns or more from a tip. The smallestcross-sectional dimension could generally be any extent such as alength, width or height dimension or any other extent that would be theshortest distance that could be drawn from one surface or face of themicrostructure to an opposing surface or face. The microstructure heightis generally 1000 microns or less, preferably 750 microns or less. Theratio of the mean foam cell size to the smallest cross-sectionaldimension is 0.75 or less, preferably 0.5 or less. The foamed articlemay be provided in a variety of shapes, including a rod, a cylinder, asheet, etc. Preferably, the foam is provided in the form of a sheet, thefoam has a pair of major surfaces, one or both of which can be providedwith surface microstructures. The foam backing and microstructures bothinclude a plurality of voids, which voids are of a mean sizesubstantially less than the smallest cross-sectional dimension or extentof the microstructures.

The foam can also comprise at least one layer in a multi-layerconstruction by a coextrusion process whereby a foam is coextruded withat least one other material, which may be a foamed or unfoamed material.For example, the foam can comprise some or all of the surfacemicrostructures with a non-foamed backing or, conversely, the foam cancomprise some or all of the backing with non-foamed surfacemicrostructures.

The coextrusion process may be used to make a foam material comprisingtwo layers or more. A layered material or article may be produced byequipping a die with an appropriate feed block, e.g., a multilayerfeedblock, or by using a multi-vaned or multi-manifold die such as a3-layer vane die available from Cloeren Corp. (Orange, Tex.). Materialsor articles having multiple adjacent foam layers may be made with foamlayers comprising the same or different materials. Foam articles of thepresent invention may comprise one or more interior and/or exterior foamlayer(s). In such a case, each extrudable, foamable material may beprocessed using one of the above-described extrusion methods whereinmelt mixtures are fed to different inlets on a multi-layer feedblock, ormulti-manifold die, and are brought together prior to exiting the die.The layers foam in generally the same manner as described above for theextrusion process. The multi-layer process can also be used to extrudethe foam of this invention with other types of materials such asunfoamed polymeric materials and any other type of polymeric material.When a multi-layered article is produced, it is preferable to formadjacent layers using materials having similar viscosities and whichprovide interlayer adhesion.

If adjacent layers of materials are heated to substantially differenttemperatures, a die can be used that will thermally isolate thedifferent materials until just prior to their exiting the die, forexample the die disclosed in U.S. Pat. No. 5,599,602. This can diminishor eliminate negative effects of contacting the different materials suchas melting or collapsing the foam or causing continued cell expansioncoalescense.

The foamable melt mix may also include additives. Examples of suitableadditives include tackifiers (e.g., rosin esters, terpenes, phenols, andaliphatic, aromatic, or mixtures of aliphatic and aromatic synthetichydrocarbon resins), plasticizers (other than physical blowing agents),nucleating agents (e.g., talc, silicon, or TiO₂), pigments, dyes,reinforcing agents, solid fillers, hydrophobic or hydrophilic silica,calcium carbonate, toughening agents, flame retardants, antioxidants,finely ground polymeric particles (e.g., polyester, nylon, orpolypropylene), glass beads, stabilizers (e.g., UV stabilizers), andcombinations thereof.

A preferred microstructure formed in the present invention is amicrostructured hook. A first method of forming foamed microstructuredhook strips with a continuous foam film-like film backing is byextruding a foamable semi-crystalline thermoplastic resin through a dieonto a continuously moving mold surface with cavities. This is generallya roll surface 3 as shown in FIG. 1. The molten foam is extruded orforced into the cavities 12 by pressure generally by use of a nip. Inthe case of FIG. 1, the nip is formed by the extruder die 8 and the roll3 but alternatively the polymer could be extruded between two rollsurfaces or the like. The nip or gap is sufficient that a film backing30 is also formed over the cavities. The film backing preferably has asmooth surface along the back but could have a textured or roughsurface. The formed material 20 has projection or hook elements 28projecting from a foam backing 30 which material is removed from themold surface by a take-up device 2. A vacuum can be used to evacuate thecavities for easier extrusion into the cavities.

The cavities 12 could be in the shape of the final hook elements asdisclosed, for example, in U.S. Pat. No. 6,174,476 or 6,540,497. In thiscase, a generally continuously tapered hook is pulled from continuouslytapered hook cavities in its final hook form or at least a partiallyformed hook element. Also, the extruded strip 20 could be a foam webprovided with only partially formed hook elements or, as shown in FIG.2, unformed hook elements forming projections. The tip portion 26 ofthese projections (or the tips of partially formed hook elements) thencould be subsequently formed into the desired finished hook elements 32.This would, in a preferred method, be done by deforming the tip portionsusing heat and/or pressure. The heat and pressure, if both are used,could be applied sequentially or simultaneously. In a preferred method,heat and pressure is selectively applied to the tip portion 26 in a nip21. In this case, there is provided a nip 21 having at least one firstheated surface member 22 and at least one second opposing surface member24. The nip has a gap which gap has a compression zone defined by afirst entry gap width and a second end gap width. The first gap width issubstantially equal to or less than the web first average thickness. Thesecond end gap width is less than the first web thickness and is thesmallest gap width of the nip 21. The final hook strip has formed hookheads 32 on the projection 28.

A specific suitable method for forming a foam having an array ofupstanding projections for use in the FIG. 2 process is shown in FIG. 1.A feed stream of preselected foamable thermoplastic resin is fed byconventional means into an extruder 6 which melts the resin and movesthe heated resin to a die 8. The die 8 extrudes the resin as a wideribbon of material onto a mold surface 3, e.g., a cylinder, having anarray of mold cavities 12 in the form of elongated holes, whichpreferably taper to facilitate removal of the solidified resin from themold cavities. These holes or mold cavities are preferably in the formof straight (i.e., only one axis in the length direction) cavities. Themold cavities can be connected to a vacuum system (not shown) tofacilitate resin flow into the mold cavities. This could require adoctor blade or knife to remove excess material extruded into theinterior face of the mold cylinder. The mold cavities 12 preferablyterminate in the mold surface having an open end for entry of the liquidresin and a closed end. In this case, a vacuum could be used to at leastpartially evacuate the mold cavities 12 prior to entering the die 8. Themold surface 3 preferably matches that of the die 8 where they are incontact to prevent excess resin being extruded out, e.g., the die sideedges. The mold surface and cavities can be air or water cooled, or thelike, prior to stripping the integrally formed backing and upstandingformed stems from the mold surface such as by a stripper roll 2. Thisprovides a web 20 of a backing 30 having integrally formed upstandingstems or hooks 28 of thermoplastic material. Alternatively, upstandingstems could be formed on a preformed backing or the like by extrusionmolding or other known techniques.

More specifically describing the FIG. 2 process, the heated calenderroll 22 contacts a predetermined portion of a distal end 26 of the stems28 projecting upward from the backing 30 to form a capped head 32. Theroll temperature will be that which will readily deform the distal ends26 under pressure created by the nips in the compression zone 38 withoutcausing resin to stick to the roll 22 surface. The roll 22 surface canbe treated with release coatings resistant to high temperature to allowfor higher temperatures and/or longer contact times between the stemtips or distal ends 26 and the heated roll 22.

The hooks are generally of uniform height, preferably from about 0.10 to1.3 mm in height, and more preferably from about 0.2 to 0.5 mm inheight. The capped stem hooks have a density on the backing preferablyof from 60 to 1,600 hooks per square centimeter, and in one preferredembodiment from about 100 to 700 hooks per square centimeter. Withcapped hooks, the stem portions have a diameter adjacent the heads ofpreferably from 0.07 to 0.7 mm, and more preferably from about 0.1 to 03mm. The capped heads project radially past the stem base portions on atleast one side, preferably two or more sides, preferably by, on average,about 0.01 to 0.3 mm, and more preferably by, on average, about 0.02 to0.25 mm and have average thicknesses between their outer and innersurfaces (i.e., measured in a direction parallel to the axis of thestems) preferably from about 0.01 to 0.3 mm and more preferably fromabout 0.02 to 0.1 mm. The capped heads have an average diameter (i.e.,measured radially of the axis of the capped heads and the stems) toaverage capped head thickness ratio preferably from 1.5:1 to 12:1, andmore preferably from 2.5:1 to 6:1.

For most hook-and-loop uses, the hooks should be distributedsubstantially uniformly over the entire surface area of the hook strip,usually in a square, staggered or hexagonal array. For hermaphroditicuses, the hooks preferably are distributed to prevent lateral slippagewhen engaged.

A second method for forming a foamed hook strip having hooks, such asthat of FIG. 4, is schematically illustrated in FIG. 3. Generally, themethod includes first extruding a strip 50 of foamable thermoplasticresin from an extruder 51 through a die 52 having an opening cut, forexample, by electron discharge machining, shaped to form the strip 50with a base and elongate spaced ribs projecting above an upper surfaceof the base layer that have the cross sectional shape of the hookportions or members to be formed. The foamed strip 50 is pulled aroundrollers 55 through a quench tank 56 filled with a cooling liquid (e.g.,water), after which the ribs (but not the base layer) are transverselyslit or cut at spaced locations along their lengths by a cutter 58 toform discrete portions of the ribs having lengths corresponding to aboutthe desired thickness of the hook portions to be formed. Optionally, thestrip can be stretched prior to cutting to provide further molecularorientation to the polymers forming the ribs and/or reduce the size ofthe ribs and the resulting hook members formed by slitting of the ribs.The cutter 58 can cut using any conventional means such as reciprocatingor rotating blades, lasers, or water jets, however preferably it cutsusing blades oriented at an angle of about 60 to 80 degrees with respectto length of the ribs.

After cutting of the ribs, the base of the strip 50 is longitudinallystretched at a stretch ratio of at least 2 to 1, and preferably at astretch ratio of about 4 to 1, preferably between a first pair of niprollers 60 and 61 and a second pair of nip rollers 62 and 63 driven atdifferent surface speeds. Optionally, the strip 50 can also betransversely stretched to provide biaxial orientation to the base.Roller 61 is preferably heated to heat the base prior to stretching, andthe roller 62 is preferably chilled to stabilize the stretched base.Stretching causes spaces between the cut portions of the ribs, whichthen become the hook portions or members 74 for the completed hookfastener portion 70.

Referring now to FIGS. 4 and 5, a hook fastener portion 10 comprises athin strong flexible film-like foamed backing 11 having generallyparallel upper and lower major surfaces 12 and 13, and a multiplicity ofspaced hook members 14 projecting from at least the upper surface 12 ofthe backing 11. The backing can have planar surfaces or surface featuresas could be desired for tear resistance or reinforcement. The hookmembers 14 each comprise a stem portion 15 attached at one end to thebacking 11 and preferably having tapered sections that widen toward thebacking 11 to increase the hook anchorage and breaking strengths attheir junctures with the backing 11, and a head portion 17 at the end ofthe stem portion 15 opposite the backing 11. The sides of the headportion 17 can be flush with the sides of the stem portion 15 on twoopposite sides. The head portion 17 has hook engaging parts or armsprojecting past the stem portion 15 on one or both sides. The hookmember has a rounded surface 18 opposite the stem portion 15 to help thehead portion 17 enter between loops in a loop fastener portion. The headportion 17 also has transverse cylindrically concave surface portions atthe junctures between the stem portion 15 and the surfaces of the headportion 17 projecting over the backing 11. The foam cell size issubstantially smaller than the smallest cross-sectional extent of themicrostructural hook element. FIG. 6 is an embodiment of a hook fastenerportion 64 formed with a foam having a cell size range that is largerthan the smallest cross-sectional extent of the hook members 65. Thehook heads 68 are misformed or nonexistent. The backing 61 is irregularand its upper and lower surfaces 62 and 63 are nonparallel and hassignificant variations in thickness.

In certain applications, it has been discovered that very low hookdensities are desirable. For example, hook densities of less than 100,preferably less than 70 and even less than 50 hook per square centimeterare desirable when used to attach to low loft nonwovens using arelatively large area flexible hook fastener tab or patch formed of afoamed hook fastener. This low spacing has been found to increase thehooking efficiency of the individual hook element, particularly relativeto low cost and otherwise ineffective nonwoven materials nottraditionally used as loop products. The hook tab or patch is also madeflexible by suitable selection of the polymer forming the base layerand/or by the stretching of the foam base layer reducing its thickness,to a preferred range of 100 μm to 25 μm. Biaxial orientation alsoreduces the hook density to the desired range for a large area hookfastener.

A large area fastener when used on a garment type application such asdiapers or the like provides stability between the two engaged regions.A suitable large area fastener would have a surface area of 5 to 100cm², preferably 20 to 70 cm².

When a large area (oversized) fastener is brought forward or backwardfor engagement with an outer surface of an article, the oversizedfastener may be capable of fastening into any portion of the outersurface of the article. With this, the need for a specific attachmentregion or target attachment zone can be eliminated if the garment canengage at some minimum level with the fastener. The larger area alsoensures secure closure due to the fasteners size. As such, large areafoamed hook fasteners of the invention could potentially eliminate theneed for a separate loop component or other “mating” fastener componenton the breathable backing of the garment or article. The increased sizeof the large area fastener also can eliminate the need for secondaryfasteners or bonded areas (such as passive bonds) that may be requiredto stabilize the overlapped regions of the article or garment.

Use of large area fastener reduces the manufacturing complexity of agarment such as an absorbent article by eliminating the need foradditional bond points or multiple fasteners to stabilize the fasteningsystem of e.g., the front and rear waist regions. The addition of bondpoints or additional fasteners increases the complexity of themanufacturing process.

Specifically, a large area hook fastener, is capable of directlyengaging an outer surface of a diaper provided with a relatively lowloft nonwoven without the need for an expensive loop patch. The largearea flexible hook fastener can also prevent inadvertent opening of theclosure due to the large contact and attachment area creating a morestable garment closure. The oversized hook fastener could also be usedin a prefastened pull-on type garment, due to its large area of largearea contact, making the garment suitably stable for packaging andsubsequent use.

Examples of suitable uses for this low hook density large area hookfastener element, as a hook tab or patch, are illustrated in FIGS. 9-12,14 and 15. In FIG. 9, a large area foam fastening tab is attached to abreathable carrier substrate 92 such as a nonwoven web, which isattached to a diaper 90 as is known in the art. The fastening tab couldbe of a size of from 5 to 100 cm², preferably 20 to 70 cm² and can beattached directly to a low loft nonwoven 94 forming the outer cover ofthe diaper 90. Typically, this low loft nonwoven would be a spunbondweb, a bonded carded or air laid web, a spunlace web or the like. FIG.10 is a variation of this fastening tab type construction for a diaper95, however, where the hook tab 96 is directly bonded to the diaper 95,either at an ear cutout portion or at the edge region of the diaper.FIG. 11 is a further embodiment of a large area hook tab 98 used with apull up type diaper design 97. In this embodiment, the hook tab 98 wouldengage a suitable mating region 99 on the opposite face of the pull updiaper. Of course, these two elements could be reversed. In both cases,the mating region could be a nonwoven used to form the nonwoven outercover of the diaper or the nonwoven fluid permeable topsheet. FIG. 12 isan embodiment of the invention hook material being used as a large areapatch 101 on a feminine hygiene article 100. The patch could be used asthe primary attachment element to the undergarment, optionally asecondary attachment element 103 could be provided on attachment wings102. The use of the low hook density element as a large area patch couldalso be used on a diaper where the patch could form a part or all of thediaper outer cover.

FIG. 13 is an example of the large area fastener 80 provided with a loopmaterial 85 on the face opposite that having the hook elements. The loopis a woven or nonwoven type loop and can be applied to the backing 81 ofthe large area hook fastener 80 by bonding 82 which can be adhesive,heat, pressure or sonic bonding combinations thereof.

This type of self-engaging fasteners 31 can be used as a wrap 33 such,as shown in FIG. 14, for use as a sport wrap. The self-engaging fastenercan also be used as a wrap for articles such as produce, where softnesswould be beneficial. FIG. 15 shows the self-engaging fastener 46 as amedical wrap which could be used with an absorbent pad 44, if desired,or use of the absorbent pad could be optional if the loop fabric wasabsorbent.

Test Methods 135 Degree Peel Test

The 135 degree peel test was used to measure the amount of force thatwas required to peel a sample of the mechanical fastener hook materialfrom a sample of loop fastener material. A 5.1 cm×12.7 cm piece of aloop test material was securely placed on a 5.1 cm×12.7 cm steel panelby using a double-coated adhesive tape. The loop material was placedonto the panel with the cross direction of the loop material parallel tothe long dimension of the panel. A 1.9 cm×2.5 cm strip of the mechanicalfastener to be tested was cut with the long dimension being in themachine direction of the web. A 2.5 cm wide paper leader was attached tothe smooth side of one end of the hook strip. The hook strip was thencentrally placed on the loop so that there was a 1.9 cm×2.5 cm contactarea between the strip and the loop material and the leading edge of thestrip was along the length of the panel. The strip and loop materiallaminate was then rolled by hand, twice in each direction, using a 1000gram roller at a rate of approximately 30.5 cm per minute. The samplewas then placed in a 135 degree peel jig. The jig was placed into thebottom jaw of an Instron™ Model 1122 tensile tester. The loose end ofthe paper leader was placed in the upper jaw of the tensile tester. Acrosshead speed of 30.5 cm per minute and a chart recorder set at achart speed of 50.8 cm per minute was used to record the peel force asthe hook strip was peeled from the loop material at a constant angle of135 degrees. An average of the four highest peaks was recorded in grams.The force required to remove the mechanical fastener strip from the loopmaterial was reported in grams/2.54 cm-width. A minimum of 10 tests wererun and averaged for each hook and loop combination.

Loop material ‘A’ was used to measure the performance of the mechanicalfastener hook materials. Loop material ‘A’ is a nonwoven loop madesimilar to that described in U.S. Pat. No. 5,616,394 Example 1,available from the 3M Company as KN-1971. The loop test material wasobtained from a supply roll of the material after unwinding anddiscarding several revolutions to expose “fresh” material. The loop testmaterial thus obtained was in a relatively compressed state and was usedimmediately in the peel test before any significant relofting of theloops could occur.

135 Degree Twist Peel Test

A 135 degree twist peel test was used to measure the amount of forcethat was required to peel a sample of the mechanical fastener hookmaterial from a sample of low profile loop fastener material. A 1.9cm×2.5 cm strip of the mechanical fastener to be tested was cut with thelong dimension being in the machine direction of the web. A 2.5 cm widepaper leader was attached to the smooth side of one end of the hookstrip. The hook materials were fastened to the low profile loop materialusing the following procedure: The hook material, with hook side down,was placed onto the low profile loop backsheet material of a diaper. A4.1 kg weight measuring 7.6 cm×7.6 cm with medium grit abrasive paper onthe bottom surface, was placed on top of the hook material. To engagethe hook with the backsheet loop material, the diaper was held securelyflat and, the weight was twisted 45 degrees to the right, then 90degrees to the left, then 90 degrees right and then 45 degrees left. Theweight was then removed and the diaper was held firm against the surfaceof a 135 degree jig stand mounted into the lower jaw of an Instron™Model 1122 tensile tester. The loose end of the paper leader attached tothe hook material was placed in the upper jaw of the tensile tester. Acrosshead speed of 30.5 cm per minute and a chart recorder set at achart speed of 50.8 cm per minute was used to record the peel force asthe hook strip was peeled from the loop material at a constant angle of135 degrees. An average of the four highest force peaks was recorded ingrams and was reported in grams/2.54 cm-width. 10 different locationswere tested on each diaper with the average of the 10 being reported inTable 4.

Loop material ‘B’ was used to measure the performance of the mechanicalfastener hook material. Loop material ‘B’ is the nonwoven side (i.e.outward facing side) of the backsheet of a Loving Touch diaper size 3.

Density and Void Content

Density of the webs was measured using ASTM D792-86. The amount ofblowing agent incorporated into the foamable polymer mixture isgenerally chosen to yield a foam having a void content in excess of 10%,more preferably in excess of 20%, as measured by density reduction;[1−the ratio of the density of the foam to that of the neatpolymer]×100. Generally, greater foam void content reduces the foamdensity, weight and material costs for subsequent end uses.

Stiffness

The conformability or stiffness of the webs was measured using theGurley Stiffness test as described in ASTM T543.

Opacity

The opacity of the webs was measured using ASTM D1746.

Cell Size and Polydispersity of Cell Size Distribution

A Leica microscope equipped with a zoom lens at a magnification ofapproximately 25× was used to take an optical micrograph of across-section of the foam. The sizes of 20 cells were measured andweight average and number average size was determined. The ratio of theweight average size to their number average size is reported as thepolydispersity of cell size distribution.

Hook Dimensions

The dimensions of the Example and Comparative Example hook materialswere measured using a Leica microscope equipped with a zoom lens at amagnification of approximately 25×. The samples were placed on a x-ymoveable stage and measured via stage movement to the nearest micron. Aminimum of 3 replicates were used and averaged for each dimension. Thebase film thickness and hook rail height was measured both before andafter the orientation step.

Example 1

A mechanical fastener hook web was made using apparatus similar to thatshown in FIG. 1. A blend of 49% polypropylene/polyethylene impactcopolymer (7C06, 1.5 MFI, Dow Chemical Corp., Midland, Mich.), 49% highmelt strength polypropylene homopolymer (FH3400, Chisso Corp. Tokyo,Japan) and 2% chemical blowing agent concentrate (FM1307H, 50%azodicarbonamide/50% LDPE, Ampacet Corp., Tarrytown, N.Y.) was extrudedwith a 6.35 cm single screw extruder (24:1 L/D) using a “humped” barreltemperature profile of 135° C.-216° C.-177° C. and a die temperature ofapproximately 204° C. Decomposition of the blowing agent into gaseousnitrogen occurred in the second zone of the extruder. The extrudate wasextruded vertically downward through a die equipped with a die liphaving an opening cut by electron discharge machining. After beingshaped by the die lip, the extrudate was quenched in a water tank at aspeed of 10.4 meter/min with the water being maintained at approximately16° C.-20° C. The resulting structure was foamed in its entirety, i.e.both the base film layer and the upstanding hook rails were foamed. Theweb was then advanced through a cutting station where the ribs (but notthe base layer) were transversely cut at an angle of 23 degrees measuredfrom the transverse direction of the web. The spacing of the cuts was254 microns. After cutting the ribs, the base of the web waslongitudinally stretched at a stretch ratio of approximately 3.5 to 1between a first pair of nip rolls and a second pair of nip rolls tofurther separate the individual hook elements to approximately 8hooks/cm. The upper roll of the first pair of nip rolls was heated to143° C. to soften the web prior to stretching. There were approximately10 rows of ribs or cut hooks per centimeter. The base film layer had athickness of approximately 230 microns. The width of the individual hookelements was approximately 520-570 microns as measured in thecross-direction of the web. The mean cell size of the foam cells was 53microns with a polydispersity index of 1.08. The cross-section of theweb is shown in FIG. 5.

Example 2

A mechanical fastener hook web was made as in Example 1 except only thebase film layer was foamed. A blend of 49% polypropylene/polyethyleneimpact copolymer (C104, 1.5 MFI, Dow Chemical), 49% high melt strengthpolypropylene homopolymer (FH3400) and 2% chemical blowing agentconcentrate (FM1307H) was extruded with a 6.35 cm single screw extruder(24:1 LD) using a “humped” barrel temperature profile of 135° C.-210°C.-177° C. and a die temperature of approximately 204° C. to form thebase film layer. 100% C104 copolymer was used to form the non-foamedhook rails and was extruded with a 3.8 cm single screw extruder (28:1LD) using a sloped barrel profile of 204° C. in the feed zone to 232° C.in the last zone. The melt streams of the two extruders were fed to athree layer coextrusion feedblock (Cloeren Co., Orange, Tex.) with thethird layer inlet blocked such that a two layer output resulted. Thefeedblock was mounted onto a 20 cm die equipped with the same profileddie lip as in Example 1. The feedblock and die were maintained at 204°C. After being shaped by the die lip, the extrudate was quenched in awater tank at a speed of 10.7 meter/min with the water being maintainedat approximately 16° C.-20° C. The web was then advanced through acutting station where the ribs (but not the base layer) weretransversely cut at an angle of 23 degrees measured from the transversedirection of the web. The spacing of the cuts was 254 microns. Aftercutting the ribs, the base of the web was longitudinally stretched at astretch ratio of approximately 3.5 to 1 between a first pair of niprolls and a second pair of nip rolls to further separate the individualhook elements to approximately 8 hooks/cm. The upper roll of the firstpair of nip rolls was heated to 143° C. to soften the web prior tostretching. There were approximately 10 rows of ribs or cut hooks percentimeter. The base film layer had a thickness of approximately 240microns. The width of the individual hook elements was approximately305-356 microns as measured in the cross-direction of the web. The meancell size of the foam cells was 61 microns with a polydispersity indexof 1.05.

Example 3

A mechanical fastener hook web was made as in Example 2 except the hookrails were foamed and the base film layer was unfoamed. A blend of 49%C104 copolymer, to 49% FH3400 polypropylene and 2% chemical blowingagent concentrate (FM1307H) was extruded with a 3.8 cm single screwextruder (28:1 L/D) using a “humped” barrel temperature profile of 135°C.-210° C.-177° C. to form the hook rails. 100% 7C06 impact copolymer(Union Carbide Corp., Danbury, Conn.) was used to form the non-foamedbase film layer and was extruded with a 6.35 cm single screw extruder(24:1 L/D) using a sloped barrel profile of 204° C. in the feed zone to232° C. in the last zone. The melt streams of the two extruders were fedto a three layer coextrusion feedblock (Cloeren Co., Orange, Tex.) withthe third layer inlet blocked such that a two layer output resulted. Thefeedblock was mounted onto a 20 cm die equipped with a profiled die lip.The feedblock and die were maintained at 204° C. After being shaped bythe die lip, the extrudate was quenched in a water tank at a speed of4.6 meter/min with the water being maintained at approximately 16°C.-20° C. The resulting structure had a non-foamed base film layer withupstanding hook rails that were foamed approximately 70% of their heightas measured from the top downward towards the base. The web was thenadvanced through a cutting station where the ribs (but not the baselayer) were transversely cut at an angle of 23 degrees measured from thetransverse direction of the web. The spacing of the cuts was 305microns. After cutting the ribs, the base of the web was longitudinallystretched at a stretch ratio of approximately 3.5 to 1 between a firstpair of nip rolls and a second pair of nip rolls to further separate theindividual hook elements to approximately 12 hooks/cm. The upper roll ofthe first pair of nip rolls was heated to 143° C. to soften the webprior to stretching. There were approximately 15 rows of ribs or cuthooks per centimeter. The base film layer had a thickness ofapproximately 165-240 microns. The width of the individual hook elementswas approximately 200 microns as measured in the cross-direction of theweb. The mean cell size of the foam cells was 50 microns with apolydispersity index of 1.03.

Example 4

A mechanical fastener hook web was made using the microreplicatedmolding process described in U.S. Pat. No. 5,845,375 and apparatussimilar to that shown in FIG. 1. A blend of 29% ultra low densitypolyethylene (AFFINITY 8200, Dow Chemical Corp.), 68% high melt strengthpolypropylene homopolymer (PROFAX PF814, Basell USA) and 2% FM1307Hchemical blowing agent concentrate was extruded with a 6.35 cm singlescrew extruder (24:1 LD) using a “humped” barrel temperature profile of143° C.-232° C.-154° C. and a die temperature of approximately 163° C.Decomposition of the blowing agent into gaseous nitrogen occurred in thesecond zone of the extruder. The extrudate was extruded verticallydownward at a linespeed of 4.3 meter/min into a nip formed by a siliconerubber covered roll and a steel roll. Nip pressure was controlled to 1.1kg/cm² (15 psi) and the temperatures of both rolls were maintained at32° C. The silicone rubber covering of the rubber roll was machined tohave cavities approximately 2300 microns in depth at a roll surfacedensity of approximately 46 cavities per square centimeter using theprocess described in U.S. Pat. No. 5,792,411. The mean cell size of thefoam cells was 58 microns with a polydispersity index of 1.07. The smallcell sizes of the foamed melt allowed for accurate replication of thecavities in the silicone rubber resulting in a foamed base film ofapproximately 1020 microns in thickness having discrete upstandingfoamed projections approximately 760 microns in height.

Comparative Example C1

A mechanical fastener hook web was made similar to Example 1 except nohigh melt strength polypropylene was used in the blended extrudate whichconsisted of 98% 7C06 copolymer and 2% FM1307H blowing agent. Theabsence of the high melt strength polypropylene resulted insignificantly larger foam cell sizes in the extrudate and as a result,replication of the die lip profile was very poor with significantfeature distortions. An optical photograph of a cross-section of the webis shown in FIG. 6.

Table 1 below shows some of the dimensions and properties of the websprior to the cutting and orientation step.

TABLE 1 Density Void Content Base Thickness Hook Rail Example (g/cm³)(%) (μm) Height (μm) 1 0.518 40 229 592 2 0.603 32.5 241 442 3 10 203546

Table 2 below shows some of the dimensions and properties of the websafter the cutting and orientation step.

TABLE 2 Density Base Thickness Hook Rail Hook Thickness Example (g/cm³)(μm) Height (μm) (μm) 1 0.444 109 541 254 2 0.442 97 648 254 3 74 439305

Table 3 below shows some additional properties of the hook materials.

TABLE 3 135 Peel 135 Twist Peel Gurley Stiffness Opacity ExampleStrength (g/cm) Strength (g/cm) (mg) (%) 1 43 16 49.6 2 10 3 44 45

1.-58. (canceled)
 59. An article comprising a base layer made ofthermoplastic polymer having at least one outer face, said outer facecontaining over at least one area a plurality of foamed hook shapedmicrostructures comprised of multiple discrete foam cells, the foamedhook shaped microstructures comprising a polyolefin, the foamed hookshaped microstructures having at least one dimension which is greaterthan 10 microns and the discrete foam cells forming the foamed hookshaped microstructures having a mean cell size less than the smallestcross-sectional dimension of the foamed hook shaped microstructuresexcluding any tips on the foamed hook shaped microstructures andmeasured at a distance of at least 10 microns from such tips.
 60. Thearticle of claim 59 wherein the smallest cross-sectional dimension ofthe foamed hook shaped microstructures is a width or thickness dimensionand is about 50 microns or more, the foamed hook shaped microstructureshave heights of generally 1000 microns or less, the ratio of the meancell size of the discrete foam cells to the smallest cross-sectionaldimension of the foamed hook shaped microstructures is 0.75 or less, thepolyolefin is at least in part a high melt strength polypropylene havinga melt strength in the range of 25 to 60 cN at 190 C. and the base layeris oriented in at least one direction.
 61. The article of claim 59wherein the smallest cross-sectional dimension of the foamed hook shapedmicrostructures is a width dimension of about 50 microns or more, thefoamed hook shaped microstructures have heights of generally 750 micronsor less, the ratio of the mean cell size of the discrete foam cells tothe smallest cross-sectional dimension of the foamed hook shapedmicrostructures is 0.5 or less, the polyolefin is at least in part ahigh melt strength polypropylene having a melt strength of 30 to 55 cNat 190 C. and the base layer is oriented in at least one direction. 62.The article of claim 59 wherein the ratio of the mean cell size of thediscrete foam cells to the smallest cross-sectional dimension of thefoamed hook shaped microstructures is 0.75 or less, and the foamed hookshaped microstructures have a minimum height of 200 microns or more. 63.The article of claim 59 wherein the ratio of the mean cell size of thediscrete foam cells to the smallest cross-sectional dimension of thefoamed hook shaped microstructures is 0.5 or less and the foamed hookshaped microstructures have a minimum height of 300 microns or more. 64.The article of claim 59 wherein the foamed hook shaped microstructureshave a minimum cross-sectional extent of 50 microns or more.
 65. Thearticle of claim 59 wherein the foamed hook shaped microstructures havea height of 200 microns or more.
 66. The article of claim 59 wherein thefoamed hook shaped microstructures have a maximum cross-sectional extentof 300 microns or less.
 67. The article of claim 59 wherein the foamedhook shaped microstructures have a maximum cross-sectional extent of 200microns or less.
 68. The article of claim 59 wherein the base layer is afoam sheet.
 69. The article of claim 68 wherein the foam sheet has athickness of from 25 to 1000 microns.
 70. The article of claim 59wherein the discrete foam cells have cell sizes of 100 microns or less.71. The article of claim 68 wherein the foam sheet has a foam cell sizeof from 2 to 100 microns.
 72. The article of claim 68 wherein the foamsheet has a foam cell size of from 5 to 50 microns and a foam cell sizepolydispersity from 1 to
 2. 73. The article of claim 59 wherein thefoamed hook shaped microstructures are about 0.1 to 1.3 mm height. 74.The article of claim 73 wherein the density of the foamed hook shapedmicrostructures is from 60 to 1000 hooks/cm².
 75. The article of claim73 wherein the foamed hook shaped microstructures have a stem portionand a head portion.
 76. The article of claim 75 wherein the head portionis a capped head which extends out from the stem on at least one side by0.01 to 0.3 mm.
 77. The article of claim 59 wherein the base layer isnon-foamed.
 78. The article of claim 59 wherein the foamed hook shapedmicrostructures are soft to the touch.